(a) Field of the Invention
The present invention is related to a keyboard electronic musical instrument of the waveshape memory type wherein waveshapes with different tone colors read out from waveshape memories are mixed together and then converted to musical tones.
(b) Description of the Prior Art
In known keyboard electronic musical instrument of the so-called waveshape memory type, waveshape memories which have stored the required waveshapes are read out by a read-out address signal corresponding to a depressed key of the keyboard, and the resulting derived waveshapes are multiplied with an envelope shape which is intended to control the amplitude of the tone to be produced, and thus a musical tone is formed.
However, a musical tone which is pronounced by a natural musical instrument such as piano, in general, constantly varies in tone color as well as in amplitude with lapse of time from the time the tone is started to be pronounced till the extinction of this tone. Thus, the pronounced sound of the natural musical instrument is accepted to be rich as a musical tone to the ears of listeners. For example, in case of a piano, the tone has, at the time the tone is initially pronounced, complicated waveshapes containing a large number of higher harmonic components. Thereafter, the number of the higher harmonic components which were initially contained in the initially pronounced tone progressively decreases, and finally at the time the tone is about to disappear, the tone has a simple waveshape containing hardly any higher harmonic component. However, in the known keyboard style electronic musical instrument of the waveshape memory type, the waveshape of a musical tone which is read out from waveshape memories as a result of depression of a key of the keyboard represents always a mere repetition of a certain fixed waveshape from the time the tone is produced till the termination of the tone, and there is no such variation of tone color with lapse of time as noted with a natural musical instrument. Thus, the musical tone which is pronounced lacks richness and is provided as a monotonous tone. (This will hereinafter be called the first technical problem.)
Furthermore, a musical tone produced by a natural musical instrument, in general, is such that the content of higher harmonic components varies with the pitches of tones. More particularly, the content of higher harmonic components is usually smaller in a musical tone of a higher pitch, whereas the content of higher harmonic components is greater in abundance in a musical tone of a lower pitch. However, in the known keyboard style electronic musical instruments of the waveshape memory type, there has not been materialized an instrument which varies in the content of higher harmonic components for tones of different pitches. (This will hereinafter be called as the second technical problem.)
In view of the inconveniences discussed above of the conventional electronic musical instruments of the waveshape memory type, there has been worked out an invention in order to solve the above-said first technical problem concerning variation of tone color and amplitude with time, and U.S. Patent Application Ser. No. 898,523 was filled by the same assignee on Apr. 20, 1978, in which said invention is disclosed. According to the invention disclosed therein, it is possible to form a musical tone waveshape such that the content of higher harmonic components varies, i.e. waveshape configuration varies, only with time after depression of a key, in the same way as is noted in a natural musical instrument, and thus it is possible to produce a musical sound which gives a rich sensation when listened to.
This priorly proposed electronic musical instrument has an overall arrangement as shown in FIG. 1 in block form.
In this FIGURE, a keyboard circuit 1 is provided for selecting a musical tone to be produced in response to the depression of a key provided in the keyboard (not shown). Output lines of the keyboard circuit 1, which are assigned to the respective keys of the instrument keyboard, are connected to the address input of a frequency information memory 2 which contains frequency information corresponding to each key. When a key of the keyboard is depressed, the keyboard circuit 1 generates the logical "1" potential on the output line assigned to the depressed key to inform the key number of the selected keys to the frequency information memory 2. Along therewith, a key-on signal KON is delivered from the keyboard circuit 1 upon depression of said key. Thus, when a key is depressed, the memory 2 is accessed with an address given by the output lines of the keyboard circuit 1, and frequency information F corresponding to the depressed key is read out from the memory 2. The frequency information F thus read out is cumulatively added with a certain modulus in an accumulator 3 at each arrival of a clock pulse .phi.. The temporary content qF (q represents an integer incrementing at each arival of the clock pulse .phi.) is used as address information in accessing a plurality of waveshape memories 4, 5 and 6. In the respective waveshape memories 4, 5 and 6, there are stored, in digital representation, different waveshapes W.sub.1, W.sub.2 and W.sub.3 as shown in FIGS. 2A, 2B and 2C, for instance. More particularly, the amplitudes for sample points of the waveshapes W.sub.1, W.sub.2 and W.sub.3 are stored in the individual addresses of the waveshape memories 4, 5 and 6, respectively. The waveshape W.sub.1 contains a large amount of higher harmonic components, and the waveshape W.sub.2 contains a smaller amount of higher harmonic components. Whereas, the waveshape W.sub.3 is a pure sinusoidal waveshape and contains substantially no higher harmonic component. All the waveshapes W.sub.1, W.sub.2 and W.sub.3 have a same fundamental frequency.
The waveshape memories 4, 5 and 6 are successively accessed with addresses designated by the temporary contents qF of the accumulator 3, so that the waveshapes W.sub.1, W.sub.2 and W.sub.3 are read out at a repetition rate corresponding to the depressed key of the keyboard. The derived waveshapes W.sub.1, W.sub.2 and W.sub.3 having different tone colors are fed to a mixing circuit which consists of multipliers 7, 8 and 9 and an adder 10 to be mixed together in this mixing circuit at a ratio dependent upon the parameters P.sub.1, P.sub.2 and P.sub.3 supplied from a parameter generating circuit 20. More particularly, the waveshapes W.sub.1, W.sub.2 and W.sub.3 which are read out from the waveshape memories 4, 5 and 6, respectively, are multiplied in the multipliers 7, 8 and 9 with the associated parameters P.sub.1, P.sub.2 and P.sub.3, respectively. The resulting outputs W.sub.i .multidot.P.sub.i (i=1,2,3) of the multipliers 7, 8 and 9 are added up by the adder 10.
The parameter generating circuit 20 for generating parameter signals P.sub.1, P.sub.2 and P.sub.3 is composed of a counter 11 and read-only memories 12, 13 and 14. The counter 11 is re-set by the key-on signal KON when said key of the keyboard is depressed, and thereafter again begins counting of the clock pulse .phi.. The respective read-only memories 12, 13 and 14 are repetitively addressed with the contents in the counter 11, thus delivering the parameter signals P.sub.1, P.sub.2 and P.sub.3. The values of the respective retrieved parameters P.sub.1, P.sub.2 and P.sub.3 vary with time in such a manner, for instance, as shown in FIG. 3.
The output of the adder 10 is multiplied, in the multiplier 16, by an envelope shape EV supplied from an envelope generator 15, the resultant signal being converted through a sound system 17 to a corresponding musical tone. Upon depression of said key, the envelope generator 15 is initiated with the key-on signal KON to generate the envelope shape EV whose value changes with time in such a manner, for example, as shown in FIG. 4. The sound system 17 includes a loud speaker, a digital-to-analog converter for converting the digital output of the multiplier 16 to an analog signal, and an amplifier assigned to drive the loud speaker in response to the analog signal.
With the musical instrument described above, it is possible to produce a musical sound whose amplitude and tone color vary with lapse of time in accordance with the values of the envelope shapes EV and the parameters P.sub.1, P.sub.2 and P.sub.3, respectively, as will be explained below by referring to FIGS. 3 and 4.
At the time t.sub.1 when a key of the instrument keyboard is depressed, the parameters will be: P.sub.1 =1, P.sub.2 =0 and P.sub.3 =0, hence the output of the adder 10 of the mixing circuit contains only the component of the waveshape W.sub.1. Accordingly, immediately after the key depression, a very colorful tone containing a large amount of higher harmonic components is produced, though the amplitude of the produced tone is suppressed very low. At the time t.sub.2 when the envelope shape EV attains one half of a maximum level AL and therefore the produced tone attains one half of the peak intensity, the parameters will be: P.sub.1 =0.5, P.sub.2 =0.5 and P.sub.3 =0, so that there is outputted from the adder 10 a composite waveshape of two waveshapes W.sub.1 and W.sub.2 mixed together at a ratio of 1:1. Accordingly, the produced musical tone contains a smaller amount of higher harmonic components. At the time t.sub.3 when the envelope shape EV and accordingly the produced musical tone have a maximum level, the parameters will be: P.sub.1 =0, P.sub.2 =1 and P.sub.3 =0. Accordingly, only the component of the waveshape W.sub.2 is delivered from the adder 10, and thus the produced musical tone represents a relatively colorful tone color. Thereafter, the parameter P.sub.2 as well as the level of the envelope shape EV will gradually become smaller with time, whereas the parameter P.sub.3 will gradually increase. At the time t.sub.4, the envelope shape EV is below the maximum level, and P.sub.1 =0, P.sub.2 =0.5 and P.sub.3 =0.5. The output of the adder 10, i.e. the produced musical tone, contains the components of the waveshapes W.sub.2 and W.sub.3 mixed at a ratio of 1:1. Thus, the produced musical tone has a relatively simple tone color, and the intensity is decreased. Thereafter, the parameter P.sub.2 gradually decreases with time, and the parameter P.sub.3 will gradually increase. At the time t.sub.5 when the envelope shape EV decreases to zero, the produced musical tone contains only the component of the waveshape W.sub.3 and thus has a simple tone color.
As such, the above-mentioned priorly proposed musical instrument is capable of producing a musical tone which is given a tone color and envelope varying only with time. In this musical instrument, however, the tone color of the produced tones is varied with time in the same manner independently of the pitch of this tone. Namely, the musical instrument proposed in this earlier application solves only the above-said first technical problem.
Also, there is another earlier U.S. Patent Application Ser. No. 773,788, now U.S. Pat. No. 4,138,915, filed on Mar. 2, 1977 by the same assignee. This earlier application mentions the desire that the second technical problem be solved. However, this application fails to provide any concrete means leading to its solution.